Conventionally, an imaging device that uses a solid state image sensor has a problem concerning image quality deterioration due to cyclic clock noise due to system or noise due to a defect in a vertical transfer register. Although the level itself of the noise is extremely low, the noise shows on a screen as fixed vertical line noise and is highly visible, resulting in significant deterioration in the image quality. Furthermore, a smear phenomenon of linear blown-out highlights occurring on the overall image at the time of imaging an object with much higher brightness than its surroundings is also one of the main causes of image quality deterioration.
A method of removing such vertical line noise is being studied, and Patent Literature 1 (Japanese Patent Laid-Open No. 7-67038) discloses a method of reducing white lines or the like and the smear by integrating (averaging) output signals of an optical black pixel part in the vertical direction (vertical OB region) of a solid sate image sensor on a per pixel basis and averaging random noise components to zero to thereby detect a fixed pattern noise signal, and subtracting the fixed pattern noise signal from output signals of an effective pixel part of the solid sate image sensor.
FIG. 4 is a block diagram showing an overview of an example configuration of a conventional imaging device at the time of performing correction of vertical line noise (hereinafter, referred to simply as “vertical line”) using a vertical OB region as described above which is an optically black region.
As shown in FIG. 4, an output signal from a solid state image sensor 1001 is amplified by an amplifier 1002, quantized by an AD converter 1003, and then input to a vertical line correction unit 1004.
The vertical line correction unit 1004 includes an OB line selector 1005, a line memory 1006, a line integrator 1007, and a subtractor 1008.
Of the signals of an effective pixel region and the signals of a vertical OB region, the OB line selector 1005 outputs only the signals of the vertical OB region. The line integrator 1007 line-integrates (averages) the signals of the vertical OB region on a per pixel basis using the line memory 1006. Random noise is thereby removed, and a correction value for one line is obtained. This correction value is stored in the line memory 1006. The line integrator 1007 reads out the correction value stored in the line memory 1006, and outputs the same to the subtractor 1008. The subtractor 1008 subtracts the correction value described above from each line signal input from the solid state image sensor 1001 on a per pixel basis. A signal from which the vertical line noise is removed (which has been corrected in terms of vertical lines) is obtained in this manner.